1. Field of the Invention
The present invention relates to a device for uniformly cooling a surface, such as human skin, to a specified temperature using a cold mist of a cryogenic fluid and a non-contact temperature sensor.
2. Description of Related Art
The use of liquified gas coolants to cool and freeze tissue has long been known. For example, dichlorotetrafluoroethane (also known as Frigiderm.RTM. or Freon 114) has been used extensively in cosmetic surgery to cool and stiffen skin properly before mechanical dermabrasion with a rotating abrasive wheel.
The hardness of the skin freeze has been shown to be critical in controlling the depth of dermabrasion and classified as either superficial (0.2-0.5 mm), moderate (0.5-1.0 mm), or deep (1.5-2.0 mm) according to Ayres {Ayres S III: Superficial chemosurgery, including combined technique, using dermabrasion, in Epstein E, Epstein E Jr, editors: Skin surgery. Springfield, Ill., 1982, Charles C Thomas, Publisher.} The skin temperatures achieved and thus the hardness of the skin is dependent upon the type of freezing agent, skin temperature prior to treatment, operating room temperature, distance of spray, pressure of spray, density of spray, angle of spray and time of spray, among other variables.
The advantage of dichlorotetrafluoroethane is that under normal conditions its maximum skin cooling temperatures is -40.degree. C., even though its boiling point is +3.8.degree. C. Ethyl chloride was an efficient skin refrigerant but had the undesirable qualities of being explosive when mixed with air, toxic to the liver, as well as capable of causing general anesthesia upon inhalation by the patient or doctor.
It has been proven that colder cryorefrigerants (ie Cryosthesia -60.degree. C. also known as dichlorodifluoromethane or Freon 12, boiling point -29.8.degree. C.) can produce maximum skin cooling temperatures of -66.degree. C. causing unwanted tissue damage and resulting in serious complications (scarring, depigmentation, infection).
Unfortunately, all of these chlorofluorocarbon refrigerants have been shown to damage the ozone layer and their use is now strictly controlled if not outright banned in many countries.
Dry ice or frozen carbon dioxide has also been used to cool the skin. However, applying dry ice to the skin's surface can quickly produce temperatures of close to -78.degree. C. "Dry ice" application has been shown to be destructive to the epithelium layer and is now more commonly used to improve the penetration of skin peeling chemicals by removing the epidermis just prior to peel-acid application. Because temperatures of -78.degree. C. are rapidly approached with little room for manual control, direct solid state, "dry ice" contact is not a viable option for controlled cooling of skin prior to or during dermabrasion if the surgeon is to minimize thermal damage. Surgeons have reported that solid carbon dioxide contact produced scarring because it was applied under pressure that occluded the, otherwise warming, local blood supply.
Cryogenic fluids such as liquid nitrogen, which pose little risk to the environment, have also been used extensively to cool surfaces. However, when sprayed on surfaces liquid nitrogen can quickly produce surface temperatures as low as -196.degree. C. Unfortunately, for many applications and in particular cosmetic surgery this low temperature can seriously damage and kill human tissue.
Given the disadvantages of current human skin cooling techniques, a need exists for a device that provides a safe and economical alternative. The present invention uses a cryogenic mist and non-contact temperature sensor to cool a surface to a desired temperature. By using a cryogenic mist, the cooling can be maintained at safe levels that allow the user to either electronically or manually control the cooling process.